Zeolite composition for use in olefinic separations

Abstract

Basically, the present invention is predicated on the discovery that zeolites that have a high silica to alumina ratio, e.g., a ratio of 20 and above, pore diameters of greater than about 5.0(Aangstroem), and which have substantially no active acid sites, i.e., zeolites which are non-reactive toward olefin isomerization and oligomerization, are especially useful in substantially separating linear olefins and paraffins from hydrocarbon mixtures containing at least linear and branched aliphatic hydrocarbons and optionally containing aromatic and other hydrocarbons.

What is claimed is: 
     
       1. A process for substantial separation of linear olefins and paraffins from mixtures containing at least linear and branched aliphatic hydrocarbons comprising: contacting the mixture with a zeolite molecular sieve having a silica to alumina ratio of greater than about 50:1, internal pore diameters of at least 5.0Å, and which has been first treated with an acid in an amount sufficient to dissolve at least some of the acid soluble impurities in the zeolite and then treated with sufficient base to neutralize the acidic impurities whereby the sieve is substantially non-reactive toward olefin isomerization and oligomerization, the contacting being conducted under conditions sufficient to effect adsorption of linear olefins and linear paraffins by the zeolite to the substantial exclusion of branched aliphatic hydrocarbons whereby the linear olefins and paraffins are substantially separated from the mixture of aliphatic hydrocarbons.   
     
     
       2. The process of claim 1 wherein the zeolite has internal pore diameters of from about 5.5Å to about 6.0Å. 
     
     
       3. The process of claim 1 wherein the zeolite has a silica to alumina ratio greater than about 100:1. 
     
     
       4. The process of claim 1 wherein the contacting is carried out in the temperature range of from about 10° C. to about 250° C. 
     
     
       5. The process of claim 4 including the step of desorbing, under the desorption conditions, the zeolite after said contacting. 
     
     
       6. The process of claim 5 wherein said zeolite is contacted with steam, under desorption conditions, in desorbing the zeolite. 
     
     
       7. A method for rendering a high silica to alumina zeolite sieve substantially non-reactive toward olefin isomerization at temperatures ranging from about 10° C. to about 150° C., comprising: washing a zeolite sieve having a silica to alumina ratio of greater than about 50:1 with an acid in an amount sufficient to dissolve at least some of the acid soluble impurities in the zeolite and then treating the acid washed zeolite with sufficient base to remove the acid impurities.   
     
     
       8. The method of claim 7 wherein the acid is aqueous hydrochloric acid and the base is aqueous sodium hydroxide. 
     
     
       9. The method of claim 7 wherein the acid is aqueous hydrochloric acid and the base is gaseous NH 3 . 
     
     
       10. The method of claim 7 wherein the acid used is aqueous hydrochloric acid in an amount sufficient to remove substantially all the acid soluble impurities in the zeolite. 
     
     
       11. A zeolite composition having reduced acid sites prepared by: washing a zeolite sieve having a silica to alumina ratio of greater than about 50:1 with an acid in an amount sufficient to dissolve at least some of the acid soluble impurities in the zeolite and then treating the acid washed zeolite with sufficient base to remove the acid impurities.